The invention relates to the field of the automotive industry. More precisely, the invention relates to brake disks of the type comprising two mutually spaced plates connected one to the other by ventilation studs.
A brake disk must be able to store the calories absorbed in the course of a braking and to return them sufficiently quickly between two successive brake applications.
The object of this is to avoid altering the coefficient of friction between the brake pad and the material of the braking track of the disk, which allows the braking distances not to be substantially altered.
Within the field of the invention, a distinction is made between “full” or “mass” disks and “ventilated” disks.
“Mass” disks are designed to store a large quantity of heat. They therefore constitute high-capacity calorie stores, the return of the calories being realized very slowly.
The drawbacks of these disks are as follows:                they constitute a relatively sizeable “unsprung” mass, rarely fully utilized;        they give rise to an overconsumption of fuel (on account of their weight);        they give rise to an energy “pollution” (through reaccumulation of calories).        
The ventilated disks comprise two plates (braking tracks) between which a heat-exchanging fluid circulates and are designed to store a small quantity of energy, with a rapid return. Although these disks are less compact then mass disks, they allow:                a reduction of the “unsprung” mass;        an optimal utilization of the thermal capacity of the disk;        decreased fuel consumption;        reduced energy pollution.        
This being the case, the ventilation elements provided between the plates must be designed (shape, arrangement) so as to make best use of the mechanical properties of the fluids with respect to the inflow and outflow of the heat-exchanging fluid.
A number of methods for ventilated disks are currently known, the ventilation thereof being obtained with a variety of means whose effectiveness is sometimes debatable and whose justification, in terms of the effect of the means applied to the ventilation, is not always clearly established.
In practice, the ventilation means are most often empirically designed and evolve in the course of the problems encountered during the production and/or the use of the parts.
According to a method illustrated by FIG. 1, the ventilation means are constituted by vanes which connect the two brake tracks and the longitudinal axis of which (viewed from above) converges toward the center of rotation of the disk. The term “vanes” is used where the length of the ventilation element has a length greater than or equal to 50% of the width of the braking track.
These vanes achieve a relatively satisfactory result in terms of the convection-based heat exchange surface.
At the same time, these vanes achieve limited results as regards their capacity to:                provide a large conduction-based heat exchange surface;        accelerate the circulation velocity of the air independently of the environment;        increase the air flow.        
On the other hand, such vanes produce very unsatisfactory results as regards their capacity to limit deformations of the track under the influence of the temperature and of the pressure applied to the disk by the brake pads.
In order to improve the performance of these vanes, one variant consists in realizing a rounded protuberance (giving the vanes the shape of a water droplet) on the side of the periphery of the disk.
According to another method illustrated by FIG. 2, the ventilation means are constituted by studs connecting the two brake tracks, with or without longitudinal axis (in the presence of longitudinal axes, these converging toward the center of rotation of the disk). The term “studs” is used where the size of the ventilation means in a radial direction is less than or equal to 50% of the width of the braking track.
As can be seen from FIG. 2, the studs 20 can have a variety of shapes; in the present case, the studs of the inner and outer rows have an oval shape, whereas the studs of the intermediate row have a diamond shape.
Such studs achieve relatively satisfactory results as regards their capacity to:                provide a large convection-based heat exchange surface;        provide a large conduction-based heat exchange surface;        accelerate the circulation velocity of the air independently of the environment;        increase the air flow;        limit the deformations of the track under the influence of the temperature and of the pressure applied to the disk by the brake pads.        
Nevertheless, the performance of such a ventilated disk is linked to the number of studs used.
Now, the increase in number of these studs gives rise to problems at the casting stage, especially in that the realization of the casting cores becomes very complex.
Moreover, with such studs it is found that these form obstacles to the pouring of the material into the casting molds, leading to a greater or lesser number of cast-offs.
According to a third solution illustrated by FIG. 3, the ventilation means comprise small columns 30, which extend from one of the tracks but without connecting the latter to the other track. It will be noted that these small columns are generally combined with studs 20 and/or vanes 10.
Such a method has limited results as regards the capacity to:                accelerate the circulation velocity of the air independently of the environment;        increase the air flow.        